Magnetic signalling in pipelines

ABSTRACT

Method systems and apparatus for signalling within pipelines. The systems methods and apparatus make use of a unit locatable within a tubular piece of metallic structure for the transmission and/or reception of signals. The unit includes a magnetic material core ( 6 ) which provides a path for magnetic flux through the unit ( 4 ). A coil ( 81 ) is wound around a portion of the magnetic material core ( 6 ) to allow the detection and/or application of magnetic flux in the magnetic core ( 6 ). At each end of the core ( 6 ) there is pair of arms ( 63 ) which are arranged for location adjacent the inside surface of the tubular structure. In use magnetic signals flowing in the tubular structure pass through the core ( 6 ) and can be detected via the coil ( 81 ) in receive mode and similarly signals flowing in the coil ( 81 ) can cause magnetic flux to flow through the core ( 6 ) and into the metallic structure in transmit mode.

This application relates to methods, systems and apparatus forsignalling in pipelines, in particular from within generally tubularmetallic structure of pipeline systems.

In a number of circumstances it is desirable to be able to communicatefrom locations on pipeline systems. Furthermore, in some cases there isa desire to communicate from a location within a piece of tubularmetallic structure, for example from within the casing of a well, orfrom within a flowline such as a production string.

Transmitting from such locations is problematic and conventionally theonly feasible way to achieve this is by making use of separate wireswhich run from the transmitter location.

The applicants have realised that it is possible to signal from withingenerally tubular metallic structure, such as well casings, usingmagnetic signals which are propagated away from the transmittinglocation either along the tubular metallic structure itself or throughsurrounding media. Similarly it is possible to signal to such locationsin a similar way.

The present invention relates to methods, systems and apparatus whichmake use of these principles.

According to a first aspect of the present invention there is provided atransmission unit for use in signalling from within generally tubularmetallic structure of a pipeline system, which unit comprises a magneticmaterial core providing a path for magnetic flux through the unitbetween two opposing end portions of the core which are arranged forlocation adjacent an inner surface of a tubular structure, andtransmitting means for causing magnetic flux to flow through the core.

When such a transmission unit is disposed in a tubular metallicstructure with the end portions adjacent the inner surface of thestructure, operating the transmitting means causes magnetic flux to flowthrough the core and an adjacent portion of the tubular structure andhence, because of flux leakage, causes magnetic signals to be propagatedaway from the transmission unit These signals may be received bydetecting means disposed at a remote location.

According to a second aspect of the invention there is provided a datatransmission method for signalling from within generally tubularmetallic structure of a pipeline system, comprising the steps of:

-   -   providing a transmission unit within the tubular structure,        which unit comprises a magnetic material core providing a path        for magnetic flux through the unit between two opposing end        portions of the core which are arranged for location adjacent an        inner surface of the tubular structure, and transmitting means        for causing magnetic flux to flow through the core;    -   operating the transmitting means to cause magnetic flux to flow        through the core and an adjacent portion of the tubular        structure; and    -   detecting, at a location remote from the transmission unit,        magnetic signals propagated away from the transmission unit.

According to a third aspect of the invention there is provided a datatransmission system for signalling from within generally tubularmetallic structure of a pipeline system, comprising:

-   -   a transmission unit disposed within the tubular structure, which        unit comprises a magnetic material core providing a path for        magnetic flux through the unit between two opposing end portions        of the core which are located adjacent an inner surface of the        tubular structure, and transmitting means for causing magnetic        flux to flow through the core, wherein operating the        transmitting means causes magnetic flux to flow through a        portion of the tubular structure adjacent the core as well as        the core itself.

The data transmission system may comprise detecting means, at a locationremote from the transmission unit, for detecting magnetic signalspropagated away from the transmission unit.

The transmission unit may comprise a casing which houses all or part ofthe magnetic material core as well as the transmitting means. However,it should be appreciated that even if the core runs externally to anycasing or no casing is present, the core can still provide a path formagnetic flux “through” the unit.

Preferably the end portions of the core have contact surfaces forcontacting with the inner surface of the tubular structure when in use.The contact surfaces may be profiled to closely match a shape of theinner surface of the tubular structure. Often the tubular structure willbe generally cylindrical and have a circular cross-section. However,many other shapes are possible and contact surfaces may be profiled tomeet these.

Each end portion may comprise a plurality of arms, each arm beingarranged to contact with the inner surface of the tubular structure at arespective position.

The respective positions may be spaced from one another. The arms of oneend portion may be arranged to contact with the tubular structure atcircumferentially spaced locations. Similarly the arms of the other endportion may be arranged to contact with the tubular structure atcircumferentially spaced locations.

The arms in each end portion may be movable between a retracted positionand an operative position. The arms may be placed in the retractedposition whilst the transmission unit is deployed and moved to theoperative position for use. The arms may be pivotally mounted on thetransmission unit. The arms may be arranged to be “bent out” or splayedinto contact with the surrounding structure.

The transmitting means may comprise a coil wound around the magneticmaterial core.

The transmission unit may comprise a pressure vessel. Part of themagnetic material core may be disposed within the pressure vessel andpart may be disposed outside of the pressure vessel. The magneticmaterial core may comprise non-laminated sections in the regions wherethe core passes from the inside to the outside of the pressure vessel.The magnetic material core may comprise composite bonded laminatedmaterial at least in the regions where the core passes from the insideto the outside of the pressure vessel.

The detecting means for receiving magnetic signals propagated away fromthe transmission unit may comprise a loop coil. The loop coil may beprovided around a remote portion of the tubular metallic structure oranother connected portion of metallic structure. In an alternative, theloop coil may be located so as to receive signals propagated through themedium surrounding the tubular metallic structure. The position andorientation of the loop coil may be chosen for convenience and/or tomaximise received signal.

The above unit, system and method may be arranged for use in wells. Thesystem may be a downhole to surface data transmission system. The methodmay be a downhole to surface data transmission method. The transmissionunit may be for use in signalling from a downhole location in a well.The pipeline system may comprise a well. The generally tubular metallicstructure from within which signals are sent may be a well casing or aflowline, in particular a production or drill string.

According to a another aspect of the present invention there is provideda receiving unit for use in receiving signals within generally tubularmetallic structure of a pipeline system, which unit comprises a magneticmaterial core providing a path for magnetic flux through the unitbetween two opposing end portions of the core which are arranged forlocation adjacent an inner surface of a tubular structure, and receivingmeans for detecting magnetic flux flowing through the core.

According to a further aspect of the invention there is provided a datareception method for receiving signals within generally tubular metallicstructure of a pipeline system, comprising the steps of:

-   -   providing a receiving unit within the tubular structure, which        unit comprises a magnetic material core providing a path for        magnetic flux through the unit between two opposing end portions        of the core which are arranged for location adjacent an inner        surface of the tubular structure, and receiving means for        detecting magnetic flux flowing through the core;    -   operating a transmitting means at a location remote from the        receiving unit to cause magnetic signals to propagate towards        the receiving unit; and    -   using the receiving unit to detect the transmitted magnetic        signals by virtue of the magnetic flux which is caused to flow        within the core.

According to yet another aspect of the invention there is provided adata reception system for receiving signals within generally tubularmetallic structure of a pipeline system, comprising:

-   -   a receiving unit disposed within the tubular structure, which        unit comprises a magnetic material core providing a path for        magnetic flux through the unit between two opposing end portions        of the core which are located adjacent an inner surface of the        tubular structure, and receiving means for detecting magnetic        flux flowing through the core, wherein in operation magnetic        flux flows through a portion of the tubular structure adjacent        the core as well as the core itself.

Many of the sub-features introduced following the first to third aspectsof the invention are equally applicable to the three aspects definedabove, changes in wording being made where necessary, for example“transmission unit” to “receiving unit”.

The transmitting unit may also comprise receiving means and thus act asa transceiving unit. Such a unit may be used as a relay station.

The present invention will now be described, by way of example only,with reference to the accompanying drawings in which:

FIG. 1 schematically shows a downhole magnetic data transmission systemsituated in a well;

FIG. 2 shows the transmission unit of the data transmission system inmore detail;

FIG. 3 shows part of the transmission unit as situated within the casingof the well;

FIG. 4 is a schematic cross-sectional view showing the transmission unitlocated within the casing; and

FIGS. 5A and 5B show an alternative configuration for the end portionsof a magnetic material core of a transmission unit of the type shown inFIG. 2.

FIG. 1 schematically shows a downhole data transmission system locatedin a well 1. The well 1 comprises a production string 2 and surroundingcasing 3.

The data transmission system comprises a data transmission unit 4disposed within the casing and detecting means 5 including a loop coil51 and receiver 52 disposed in a position remote from the datatransmission unit 4.

FIG. 2 shows the data transmission unit 4 in more detail. The datatransmission unit 4 comprises a casing 41 which provides a pressurevessel 42 for protecting the contents from the ambient pressure andhaving pressure bulkheads 43 at each end.

The transmission unit 4 further comprises a magnetic material core 6which provides a path for magnetic flux through the transmission unit 4.A central part of the magnetic material core 61 is provided within thepressure vessel 42. This central portion of the core 61 compriseslaminated magnetic material. At either end of this central portion ofthe magnetic core 61, non-laminated sections of the core 62 are providedand these pass through the respective pressure bulkheads 43 to theexterior of the pressure vessel 42. Beyond each non-laminated section ofthe core 62 there is provided a respective end portion of the core 63.

In the present embodiment, the end portions of the core 63 each comprisea respective pair of deployable arms 63 a which are pivotally mounted tothe transmission unit 4 and may be moved between a retracted position asshown in dotted lines in FIG. 2 and an extended, operative, position asshown in solid lines in FIG. 2.

Each of the arms 63 a, is formed of laminated magnetic material and hasa respective contact surface 63 b which is arranged for contact with theinternal curved surface of the surrounding tubular structure, in thisembodiment, the surrounding well casing 3. As more clearly seen in FIGS.3 and 4 the contact surfaces 63 b are profiled so as to closely matchthe curvature of the inner surface of the surrounding well casing 3.This serves to ensure that close and efficient contact is achievedbetween the arms 63 a and the surrounding well casing 3.

It will be noted that when the arms 63 a are in their retractedpositions their overall diameter is slightly smaller than that of thecasing itself. On the other hand, when the arms 63 a are in theirextended positions, the contact surfaces 63 b on the arms 63 a in eachpair are spaced by a distance which is significantly greater than thediameter of the transmission unit casing 41. This significantly aids inthe installation of the transmission unit 4, and facilitates it beingpassed along a tubing of internal diameter significantly smaller thanthe tubing where the transmission unit is to be eventually located. Thearms 63 a may also be later retracted into the position shown in dottedlines in FIG. 2, and of course this can be of assistance in removal andrecovery of the transmission unit from its installed location.

An attachment point 7 is provided at one end of the transmission unit 4.This attachment point is used for connection to a wire line or otherdeployment system used when installing or recovering the transmissionunit.

An electronics, battery and sensor module 8 is provided within thepressure vessel 42. A coil 81 is wound around part of the centralportion of the magnetic material core 61. Together with componentswithin the electronics battery and sensor module 8, the coil 81 forms atransmitting means for causing magnetic flux to flow within the magneticmaterial core 6 to allow signalling away from the transmission unit 4.

The electronics, battery and sensor module 8, and the central portion 61of the magnetic core are arranged to give a compact structure such thatthe diameter of the casing 41 can be kept to a minimum and the maximumusage of available space is made.

To achieve this it will be noted that the magnetic core 6 has a greaterdiameter in the region of the coil 81 than in the region adjacent to theelectronics, battery and sensor module 8.

In a development of the structure shown in the drawings, the magneticcore 6 may be constructed as a hollow cylinder and the electronics,battery and sensor module 8 located within that cylinder. In eithercase, the magnetic core 6 may be of a diameter substantially equal tothe internal diameter of the casing 41 and be tapered inwards in theregion of the coil 81 to provide accommodation space for the wires ofthe coil 81.

In operation, the transmitting means comprising electronics in themodule 8 and the coil 81, are used to induce magnetic flux in thecentral portion 61 of the core 6. This flux then flows through the wholeof the core, including the end portions 63, and hence comes into contactwith the surrounding well casing 3. At this point some of the flux flowsthrough the portion of well casing 3 between the end portions 63 of thecore 6 completing a magnetic circuit, but other flux escapes both intothe surrounding media (typically rock) and along the well casing 3 awayfrom the transmission unit 4. To maximise the effectiveness of thistechnique attempts can be made to saturate (in the magnetic sense) thesteel of the well casing 3 in the region between the end portions 63 ofthe core 6.

In the present embodiment, data transmission is achieved by making useof the flux which escapes through the surrounding media. This flux ispicked up by the detecting means 5 positioned at the surface. In thisway data may be sent from the data transmission unit 4, disposed withinthe well casing 3, to the surface. The data transmitted may typicallyconsist of measurements taken by sensors provided within the datatransmission unit 4.

In an alternative, a loop coil of a type similar to that shown in FIG.1, may be positioned around the tubular metallic structure at thesurface or metallic structure connected to the tubular structure, inthis case the well head. In such a case signals may be received byvirtue of the flux which travels along the well casing 3 (and possiblyother metallic structure) away from the transmission unit 4.

The frequency of magnetic signals to be used will typically bedetermined empirically based on those that give best results. Wheresignals are detected having travelled through the surrounding media, thecharacteristics of the media will dictate what frequencies work best. Itis to be expected in most cases however, that low frequency signals, sayin the order of a few 10s of Hz will be effective. Often only low datarates are required, of say a few bits/s.

It will be noted that in the present embodiment a pair of arms are usedin each end portion of the magnetic material core 6. However, this isnot essential. It is envisaged that other numbers of arms could be used,and indeed entirely different end portion structures might be used. Whatis important is that a pair of opposing end portions are provided whichcan be located adjacent to the inner surface of the surrounding tubularstructure. Of course there is no need for such end portions to bepivotally mounted, this merely serves to ease deployment and recovery ofthe transmission unit 4. Similarly, different arrangements for the wholeof the magnetic core 6 can be envisaged and in some circumstances it maybe possible to do away with the pressure vessel 42 and/or the whole ofthe transmission unit casing 41. As an example the magnetic core 6 andassociated coil 81 can be housed separately and/or deployed/recoveredseparately from the electronics and other components.

FIGS. 5A and 5B show an alternative form of end portion 63 which may beused in place of the pivoting arm structure shown in FIG. 2. In thiscase the arms 63 b of the end portion 63 are arranged to move between aretracted position, as shown in FIG. 5A, and a splayed (deployed)position, as shown in FIG. 5B, by bending. A deployment cone 63 c isprovided which is pulled inbetween the arms 63 b, in the direction shownby the arrow in FIG. 5B, to drive the arms 63 b outward to theirdeployed position and hence into contact with the surrounding tubularstructure.

When inserted and in operation, the transmission unit 4 can beconsidered to act as a transmitting magnetic dipole.

The arrangement used in the present embodiment where the detecting meansis arranged for receiving signals transmitted through the surroundingmedia is particularly suitable where a well is horizontal or includes asubstantial horizontal displacement from the well head. On the otherhand the alternative arrangement, where the detecting means is locatedaround the well head, is more suitable where a well is essentiallyvertical.

To some extent the range at which signals may be received, particularlywhen using the arrangement of the preferred embodiment, can be improvedby increasing the diameter of the loop coil and/or the number of turns.

One advantage of a magnetic system of this kind is that the relevantmagnetic properties of the magnetic material core 6 can be chosen to bevastly different from the steel of the pipeline infrastructure. Inparticular the magnetic material in the core might be selected to have arelative permeability which is much higher than that of the steel—thedifference might be a factor of 103 or 105.

Although not described in detail, it should be appreciated that a unithaving a structure substantially the same as that shown in the drawingsand described above may be used for the reception of signals as well asand/or in alternative to the sending of signals. A receiving unit willhave the same general structure as that described above but the coil 81will have associated electronics which together act as receiving means.A transceiving unit, able to both transmit and receive, will have bothtransmitting means and receiving means. In such a case many of thecomponents of the system may be used in both transmit and receive mode.In particular only a single core 6 is likely to be provided and a singleor separate coils 81 may be provided as a matter of design choice.

In receive mode, signals will be picked up by virtue of flux flowingalong the metallic structure (which may be applied by a similar, butremote, transmission unit). In such a case a large portion of the fluxreaching the receiving unit will travel along the magnetic core 6,because the core 6 offers a much better path for the flux than thesurrounding steel. The flux flowing in the core will induce a current inthe coil 81 which can be detected.

A transceiver unit might be used as a relay station.

A pair of transceiver units might be used either side of a break in themetallic structure of a well (caused for example by a certain type ofjoin or branch). Such an arrangement may provide a link such that acontinuous communication path from the isolated section of thestructure, to the surface is achieved. Apart from the link another typeof signalling, for example electrical signalling along the structure,might be used.

It will be noted that transmitting and receiving units of the presentsystem are locatable wholly within conductive tubing. Further nomodification to the tubing in the region of the unit is required. Thismeans that the units can be used in tubing of existing installations(even when the tubing is continuous) and indeed means that there islittle limitation on the location from or to which data is sent.Further, because of the signalling technique used, at least in somecases, it is possible to signal from within say a (metallic) drillstring even if the string is surrounded by metallic casing at the pointfrom which signals are to be sent.

1. A transmission unit for use in signalling from within generallytubular metallic structure of a pipeline system, which unit comprises amagnetic material core providing a path for magnetic flux through theunit between two opposing end portions of the core which are arrangedfor location adjacent an inner surface of a tubular structure, and atransmitter for causing magnetic flux to flow through the core, whereinthe end portions of the core have contact surfaces for contacting withthe inner surface of the tubular structure when in use.
 2. Atransmission unit according to claim 1 which is arranged for locationwholly within a tubular structure from within which signals are to besent.
 3. A transmission unit according to claim 2 which is arranged tobe operable from within an existing continuous tubular structure andwithout modification to the existing continuous tubular structure.
 4. Atransmission unit according to claim 1 comprising a casing which housesat least part of the magnetic material core as well as the transmitter.5. A transmission unit according to claim 1 in which the contactsurfaces are profiled to closely match a shape of the inner surface ofthe tubular structure.
 6. A transmission unit according to claim 1 inwhich each end portion comprises a plurality of arms, each arm beingarranged to contact with the inner surface of the tubular structure at arespective position.
 7. A transmission unit according to claim 6 inwhich the arms of one end portion may be arranged to contact with thetubular structure at circumferentially spaced locations.
 8. Atransmission unit according to claim 6 in which the arms in each endportion are movable between a retracted position and an operativeposition.
 9. A transmission unit according to claim 1 in which thetransmitter comprises a coil wound around the magnetic material core.10. A transmission unit according to claim 1 which comprises a pressurevessel where part of the magnetic material core is disposed within thepressure vessel and part is disposed outside of the pressure vessel andthe magnetic material core comprises non-laminated sections in theregion where the core passes from the inside to the outside of thepressure vessel.
 11. A transmission unit according to claim 1 whichfurther comprises a receiver and thus may act as a transceiving unit.12. A data transmission method for signalling from within generallytubular metallic structure of a pipeline system, comprising the stepsof: providing a transmission unit according to claim 1 within thetubular structure so that the end portions of the core are adjacent aninner surface of the tubular structure with the contact surfaces incontact with said inner surface; operating the transmitting means tocause magnetic flux to flow through the core and an adjacent portion ofthe tubular structure; and detecting, at a location remote from thetransmission unit, magnetic signals propagated away from thetransmission unit.
 13. A data transmission system for signalling fromwithin generally tubular metallic structure of a pipeline system,comprising: a transmission unit according to claim 1 disposed within thetubular structure so that the end portions of the core are locatedadjacent an inner surface of the tubular structure with the contactsurfaces in contact with said inner surface, wherein operating thetransmitter causes magnetic flux to flow through a portion of thetubular structure adjacent the core as well as the core itself.
 14. Adata transmission system according to claim 13 comprising a detector, ata location remote from the transmission unit, for detecting magneticsignals propagated away from the transmission unit.
 15. A datatransmission system according to claim 14 wherein the detector forreceiving magnetic signals propagated away from the transmission unitcomprises a loop coil.
 16. A receiving unit for use in receiving signalswithin generally tubular metallic structure of a pipeline system, whichunit comprises a magnetic material core providing a path for magneticflux through the unit between two opposing end portions of the corewhich are arranged for location adjacent an inner surface of a tubularstructure, and a receiver for detecting magnetic flux flowing throughthe core, wherein the end portions of the core have contact surfaces forcontacting with the inner surface of the tubular structure when in use.17. A receiving unit according to claim 16 which is arranged forlocation wholly within a tubular structure within which signals are tobe received.
 18. A receiving unit according to claim 17 which isarranged to be operable from within an existing continuous tubularstructure and without modification to the existing continuous tubularstructure.
 19. A receiving unit according to claim 16 comprising acasing which houses at least part of the magnetic material core as wellas the receiver.
 20. A receiving unit according to claim 16 in which thecontact surfaces are profiled to closely match a shape of the innersurface of the tubular structure.
 21. A receiving unit according toclaim 16 in which each end portion comprises a plurality of arms, eacharm being arranged to contact with the inner surface of the tubularstructure at a respective position.
 22. A receiving unit according toclaim 21 in which the arms of one end portion may be arranged to contactwith the tubular structure at circumferentially spaced locations.
 23. Areceiving unit according to claim 21 in which the arms in each endportion are movable between a retracted position and an operativeposition.
 24. A receiving unit according to claim 16 in which thereceiving means receiver comprises a coil wound around the magneticmaterial core.
 25. A receiving unit according to claim 16 whichcomprises a pressure vessel where part of the magnetic material core isdisposed within the pressure vessel and part is disposed outside of thepressure vessel and the magnetic material core comprises non-laminatedsections in the region where the core passes from the inside to theoutside of the pressure vessel.
 26. A data reception method forreceiving signals within generally tubular metallic structure of apipeline system, comprising the steps of: providing a receiving unitaccording to claim 16 within the tubular structure, so that the endportions of the core are adjacent an inner surface of the tubularstructure with the contact surfaces in contact with said inner surface;operating a transmitter at a location remote from the receiving unit tocause magnetic signals to propagate towards the receiving unit; andusing the receiving unit to detect the transmitted magnetic signals byvirtue of the magnetic flux which is caused to flow within the core. 27.A data reception system for receiving signals within generally tubularmetallic structure of a pipeline system, comprising: a receiving unitaccording to claim 16 disposed within the tubular structure so that endportions of the core are located adjacent an inner surface of thetubular structure with the contact surfaces in contact with said innersurface, wherein in operation magnetic flux flows through a portion ofthe tubular structure adjacent the core as well as the core itself. 28.A transmission unit for use in signalling from within generally tubularmetallic structure of a pipeline system, which unit comprises a magneticmaterial core providing a path for magnetic flux through the unitbetween two opposing end portions of the core which are arranged forlocation adjacent an inner surface of the generally tubular structurefrom which signals are to be sent, and a transmitter for causingmagnetic flux to flow through the core, wherein the transmission unit isarranged for location wholly within the generally tubular structure fromwhich signals are to be sent.
 29. A transmission unit for use insignalling from within generally tubular metallic structure of apipeline system, which unit comprises a magnetic material core providinga path for magnetic flux through the unit between two opposing endportions of the core which are arranged for location adjacent an innersurface of a tubular structure, and transmitting means for causingmagnetic flux to flow through the core, wherein the end portions of thecore have contact surfaces for contacting with the inner surface of thetubular structure when in use.
 30. A receiving unit for use in receivingsignals within generally tubular metallic structure of a pipelinesystem, which unit comprises a magnetic material core providing a pathfor magnetic flux through the unit between two opposing end portions ofthe core which are arranged for location adjacent an inner surface of atubular structure, and receiving means for detecting magnetic fluxflowing through the core, wherein the end portions of the core havecontact surfaces for contacting with the inner surface of the tubularstructure when in use.